1. Field of the Invention
The present invention relates to a surface lighting apparatus suitable for use for backlighting of a liquid crystal display panel.
2. Description of the Prior Art
A conventional surface lighting apparatus, for example, shown in Japanese Unexamined Utility Model Publication Sho No. 62-69281 is described referring to FIGS. 9 and 10. FIG. 9 is a perspective view showing the conventional surface lighting apparatus and a liquid crystal display panel. FIG. 10 shows the luminance distribution of light in the conventional surface lighting apparatus.
In FIG. 9, the conventional surface lighting apparatus comprises: a light guide 3; incandescent lamps 7a, 7a, 7b and 7b which are provided in the vicinity of end faces 3a, 3a of the light guide 3; and a reflection frame 4 for enclosing the incandescent lamps 7a7a, 7b and 7b and the light guide 3. In front of the light guide 3, a liquid crystal display panel 1 is disposed.
Light beams irradiated from the incandescent lamps 7a, 7a, 7b and 7b come into the light guide 3 and are diffusively reflected in the light guide 3 by a diffusive reflection layer 5 formed on back face of the light guide 3. The reflected light beams are irradiated from the front face 3b of the light guide 3. Thereby, the liquid crystal display panel (LCD) 1 is backlighted.
In the above-mentioned conventional surface lighting apparatus, the incandescent lamp 7a is disposed, for example, as shown in FIG. 10, wherein lengthwise direction of a filament thereof is parallel to a side face 3a of the light guide 3. In such a case, luminance distribution of the incandescent lamp 7a is shown by dotted line A in FIG. 10 (on the dotted line A, intensity of the light is even). In the vicinity of the side face 3a of the light guide 3 to the incandescent lamp 7a, quantity of incidence light is large. In the distant part from the incandescent lamp 7a, quantity of incidence light is small. As a result, distribution of the incidence light becomes as shown by dotted line B in FIG. 10 (on the dotted line B, intensity of the light is even). Namely, irradiaton of the light in the vicinity of the light guide 3 to the incandescent lamp 7a is strong and that in the distance is weak. Therefore, surface lighting becomes uneven. Furthermore, in the lengthwise direction of the conventional light guide 3, intensity of the light becomes weak responding to increase of the distance from the light source, so that illuminance as a whole of the light guide 3 becomes uneven.